To meet a demand for an improved performance of a magnetic disk apparatus, there have been active developments on technologies to increase the capacity and the data transfer speed.
Among those is the use of a thin-film magnetic head in place of a conventional monolithic type ferrite head as a head which is positioned to face the surface of a rotating magnetic disk to write and read data, thereby easily accomplishing larger capacity and higher data transfer.
That is, the use of a thin-film magnetic head can make the head smaller, reduce the inductance of the winding and increase the resonance frequency, thus narrowing the bit interval.
Therefore, the S/N of the readout signal is improved so that the recording density can be improved, making it possible to easily accomplish a larger capacity.
FIG. 1 is a schematic transverse cross section of a magnetic disk apparatus that uses this thin-film magnetic head.
In FIG. 1, "10" denotes a plurality of magnetic disks provided on a shaft 12 that is rotated by a spindle motor 11. Sliders 15 having thin-film magnetic heads 1 at their end are arranged to face the top and back surfaces of the magnetic disks 10.
Each slider 15 is attached to a spring arm 17 by a gimbal 16, and the spring arm 17 is coupled to a voice coil motor 19 via a drive arm 18.
Therefore, each thin-film magnetic head 1 is moved in the radial direction of the associated magnetic disk 10 by the voice coil motor 19 to seek the cylinder position to be accessed.
FIG. 2 is an enlarged view of the thin-film magnetic head provided at the end of the slider 15 that is supported by the gimbal 16. As shown in FIG. 2(A), the thin-film magnetic head 1 faces the magnetic disk 10 and is provided at the end of the slider 15, which has an air receiving face 151.
FIG. 2(B) presents an enlarged illustration of the thin-film magnetic head 1 provided at the end of the slider 15. The thin-film magnetic heads 1 comprise yokes 101 and coils 102. The feature lies in that those are formed by an IC process to have a thickness on the order of several microns.
The technology of designing the thin-film magnetic heads formed by this IC process is described on pages 353 to 364 in the magazine "FUJITSU Sci. Tech. J., (February 1991)."
FIG. 3 is a schematic transverse cross-sectional view as viewed from the direction of the write/read gap g (FIG. 2(B)) defined between a pair of magnetic poles (poles) of the yoke 101 of the thin-film magnetic head 1.
As shown in FIG. 3(A), the coil 102 runs through between a lower pole 103 and an upper pole 104 located at the end of the slider 15.
FIG. 3(B) further presents an enlarged illustration of the write/read gap g that is defined by the lower pole 103 and upper pole 104 facing each other.
While this thin-film magnetic head 1 can increase the track density of a magnetic disk apparatus as described earlier, it produces a peculiar negative edge.
FIG. 4 is a diagram for explaining this negative edge while comparing the gap portion g of the thin-film magnetic head 1 in FIG. 3(B) with that of the conventional monolithic type ferrite head.
As shown in FIG. 4(A), the conventional ferrite head 1 comprises a yoke 101 at the end of a slider 15 and a coil 102 wound around the yoke.
This ferrite head has a pole-face length (pole length) on the order of millimeters as shown in an enlarged view of the gap portion g in FIG. 4(B). This pole length can be considered as substantially infinite, compared with the gap distance g between the magnetic poles, so that a negative edge will not appear on the reproduced waveform (see the reproduced waveform in FIG. 4(C)).
FIG. 4(D) is an enlarged view of the gap portion g of the thin-film magnetic head 1. The pole-face length (pole length) pl 1 and pl 2 , unlike that of the ferrite head (FIG. 4(B)), are on the order of microns. Therefore, the pole-face lengths pl 1 and pl 2 should be considered as finite in comparison with the gap length g.
As the pole length pl of the thin-film magnetic head 1 is finite, a negative edge or a negative peak of the opposite phase to that of the main peak (see the NE portions of the reproduced waveform in FIG. 4(E)) occurs at positions corresponding to the outer edge portions of the poles.
This negative edge becomes a peculiar pulse (extra pulse) in the reproduced signal from a magnetic medium or reduces the signal peak (level down) in accordance with a change in the interval between reversals of magnetization, thus increasing the data read error.
As the circumferential speed of the magnetic disk differs depending on the cylinder position (the position in the radial direction of the magnetic disk 10), the time length .pi. 2 of the negative edge from the position of the normal signal peak varies. Thus, the influence of the negative edge on the reproduced signal varies also in accordance with the cylinder position.
In this respect, there is a demand for a reproduced waveform equalizing technology to effectively eliminate the negative edge peculiar to the thin-film magnetic head 1.